Vascular occlusions (clots or thrombi and occlusional deposits, such as calcium, fatty deposits, or plaque), result in the restriction or blockage of blood flow in the vessels in which they occur. Occlusions result in oxygen deprivation (“ischemia”) of tissues supplied by these blood vessels. Prolonged ischemia results in permanent damage of tissues which can lead to myocardial infarction, stroke, or death. Targets for occlusion include coronary arteries, peripheral arteries and other blood vessels. The disruption of an occlusion or thrombolysis can be effected by pharmacological agents and/or or mechanical means. However, many thrombolytic drugs are associated with side effects such as severe bleeding which can result in cerebral hemorrhage. Mechanical methods of thrombolysis include balloon angioplasty, which can result in ruptures in a blood vessel, and is generally limited to larger blood vessels. Scarring of vessels is common, which may lead to the formation of a secondary occlusion (a process known as restenosis). Another common problem is secondary vasoconstriction (classic recoil), a process by which spasms or abrupt closure of the vessel occurs. These problems are common in treatments employing interventional devices. In traditional angioplasty, for instance, a balloon catheter is inserted into the occlusion, and through the application of hydraulic forces in the range of ten to fourteen atmospheres of pressure, the balloon is inflated. The non-compressible balloon applies this significant force to compress and flatten the occlusion, thereby operating the vessel for blood flow. However, these extreme forces result in the application of extreme stresses to the vessel, potentially rupturing the vessel, or weaking it thereby increasing the chance of post-operative aneurysm, or creating vasoconstrictive or restenotic conditions. In addition, the particulate matter isn't removed, rather it is just compressed. Other mechanical devices that drill through and attempt to remove an occlusion have also been used, and create the same danger of physical damage to blood vessels.
Ultrasonic probes are devices which use ultrasonic energy to fragment body tissue (see, e.g., U.S. Pat. Nos. 5,112,300; 5,180,363; 4,989,583; 4,931,047; 4,922,902; and 3,805,787) and have been used in many surgical procedures. The use of ultrasonic energy has been proposed both to mechanically disrupt clots, and to enhance the intravascular delivery of drugs to clot formations (see, e.g., U.S. Pat. Nos. 5,725,494; 5,728,062; and 5,735,811). Ultrasonic devices used for vascular treatments typically comprise an extracorporeal transducer coupled to a solid metal wire which is then threaded through the blood vessel and placed in contact with the occlusion (see, U.S. Pat. No. 5,269,297). In some cases, the transducer is delivered to the site of the clot, the transducer comprising a bendable plate (see, U.S. Pat. No. 5,931,805).
The ultrasonic energy produced by an ultrasonic probe is in the form of very intense, high frequency sound vibrations which result in powerful chemical and physical reactions in the water molecules within a body tissue or surrounding fluids in proximity to the probe. These reactions ultimately result in a process called “cavitation,” which can be thought of as a form of cold (i.e., non-thermal) boiling of the water in the body tissue, such that microscopic bubbles are rapidly created and destroyed in the water creating cavities in their wake. As surrounding water molecules rush in to fill the cavity created by collapsed bubbles, they collide with each other with great force. This process is called cavitation and results in shock waves running outward from the collapsed bubbles which can wear away or destroy material such as surrounding tissue in the vicinity of the probe.
Some ultrasonic probes include a mechanism for irrigating an area where the ultrasonic treatment is being performed (e.g., a body cavity or lumen) to wash tissue debris from the area. Mechanisms used for irrigation or aspiration described in the art are generally structured such that they increase the overall cross-sectional profile of the probe, by including inner and outer concentric lumens within the probe to provide irrigation and aspiration channels. In addition to making the probe more invasive, prior art probes also maintain a strict orientation of the aspiration and the irrigation mechanism, such that the inner and outer lumens for irrigation and aspiration remain in a fixed position relative to one another, which is generally closely adjacent the area of treatment. Thus, the irrigation lumen does not extend beyond the suction lumen (i.e., there is no movement of the lumens relative to one another) and any aspiration is limited to picking up fluid and/or tissue remnants within the defined distance between the two lumens.
Another drawback of existing ultrasonic medical probes is that they typically remove tissue slowly in comparison to instruments which excise tissue by mechanical cutting. Part of the reason for this is that most existing ultrasonic devices rely on a longitudinal vibration of the tip of the probe for their tissue-disrupting effects. Because the tip of the probe is vibrated in a direction in line with the longitudinal axis of the probe, a tissue-destroying effect is only generated at the tip of the probe. One solution that has been proposed is to vibrate the tip of the probe in a transverse direction-i.e. perpendicular to the longitudinal axis of the probe, in addition to vibrating the tip in the longitudinal direction. For example, U.S. Pat. No. 4,961,424 to Kubota, et al. discloses an ultrasonic treatment device which produces both a longitudinal and transverse motion at the tip of the probe. The Kubota, et al. device, however, still relies solely on the tip of the probe to act as a working surface. Thus, while destruction of tissue in proximity to the tip of the probe is more efficient, tissue destruction is still predominantly limited to the area in the immediate vicinity at the tip of the probe. U.S. Pat. No. 4,504,264 to Kelman discloses an ultrasonic treatment device which improves the speed of ultrasonic tissue removal by oscillating the tip of the probe in addition to relying on longitudinal vibrations. Although tissue destruction at the tip of the device is more efficient, the tissue destroying effect of the probe is still limited to the tip of the probe.
There is a need in the art for improved devices, systems, and methods, for treating vascular diseases, particularly stenotic diseases which occlude the coronary and other arteries. In particular, there is a need for methods and devices for enhancing the performance of angioplasty procedures, where the ability to introduce an angioplasty catheter through a wholly or partly obstructed blood vessel lumen can be improved. There is also a need for mechanisms and methods that decrease the likelihood of subsequent clot formation and restenosis.